Regulation of mTORC1 by lysosomal calcium and calmodulin.

Ruo-Jing Li,Jing Xu,Yujun George Zheng,Chenglai Fu,Hao Jia,Jing Zhang,Jun O Liu

doi:10.7554/elife.19360

Ruo-Jing Li, Jing Xu + Show 5 more

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https://doi.org/10.7554/elife.19360

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Abstract

Blockade of lysosomal calcium release due to lysosomal lipid accumulation has been shown to inhibit mTORC1 signaling. However, the mechanism by which lysosomal calcium regulates mTORC1 has remained undefined. Herein we report that proper lysosomal calcium release through the calcium channel TRPML1 is required for mTORC1 activation. TRPML1 depletion inhibits mTORC1 activity, while overexpression or pharmacologic activation of TRPML1 has the opposite effect. Lysosomal calcium activates mTORC1 by inducing association of calmodulin (CaM) with mTOR. Blocking the interaction between mTOR and CaM by antagonists of CaM significantly inhibits mTORC1 activity. Moreover, CaM is capable of stimulating the kinase activity of mTORC1 in a calcium-dependent manner in vitro. These results reveal that mTOR is a new type of CaM-dependent kinase, and TRPML1, lysosomal calcium and CaM play essential regulatory roles in the mTORC1 signaling pathway.

Highlights

Mechanistic target of rapamycin plays an essential role in sensing a myriad of environmental cues including nutrients and growth factor stimulation to regulate cell growth and proliferation (Wullschleger et al, 2006). mTOR independently associates with raptor or rictor to form two distinct complexes, mTORC1 and mTORC2, respectively
To determine whether TRPML1 is required for mTORC1 signaling, HEK293T cells were transduced with lentiviral shRNA targeting human TRPML1 (Sh1 and Sh2) or a scrambled shRNA (Scr)
Integrating our previous observations (Xu et al, 2010) and the results from the present study, we propose an addition to the current model of mTOR signaling pathway: upon the translocation of mTORC1 onto the lysosome, properly released lysosomal calcium enriches local Ca2+ concentration, prompting Ca2+ binding to a local population of CaM, which in turn binds mTORC1 and stimulates the kinase activity of the mTORC1 complex

Summary

Introduction

Mechanistic target of rapamycin (mTOR) plays an essential role in sensing a myriad of environmental cues including nutrients and growth factor stimulation to regulate cell growth and proliferation (Wullschleger et al, 2006). mTOR independently associates with raptor or rictor to form two distinct complexes, mTORC1 and mTORC2, respectively. PRAS40 are specific to mTORC1, whereas rictor, mSin protor1/2 are unique to mTORC2 (Laplante and Sabatini, 2012). These two complexes differ in their sensitivity to rapamycin, upstream signals and downstream outputs (Laplante and Sabatini, 2012). The mTORC1 complex integrates different extracellular and intracellular signal inputs, such as growth factors, amino acids, stress and energy status, to regulate cellular processes such as protein and lipid synthesis and autophagy, by phosphorylating and activating p70 S6 kinase (p70S6K) (Chung et al, 1992; Price et al, 1992) and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) (Lin et al, 1995; von Manteuffel et al, 1996). MTORC2 is involved in Akt phosphorylation and regulation of the cellular cytoskeleton

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